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arXiv · 2608.22985

What Does Activation Steering Control? Attribution Across Answer Encodings and Output-Sensitive Subspaces

Zhiwei Gao·Shaowen Peng·Shoko Wakamiya·Eiji Aramaki
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Abstract

Activation steering is often evaluated under the answer encoding used to construct the direction. A reported gain may reflect the intended judgment or compatibility with answer identifiers seen during construction. We introduce Cross-Encoding Steering Evaluation, which freezes an intervention while re-encoding answers to the same held-out items. On NormBank, after A/B/C identifiers are reassigned, contrastive activation addition (CAA) induces larger target-versus-source score changes for the extraction indices than for the semantic labels under the new mapping. We call this extraction-index following. Varying identifier vocabulary (A/B/C, X/Y/Z, or 1/2/3) and row order shows that the effect tracks extraction index rather than row position. After matching direction norms across layers, extraction-index following emerges mainly at later depths. A low-rank output-sensitive component containing 15.4% of the direction's squared norm retains 96.3% of this effect. An Inference-Time Intervention (ITI)-style method also favors extraction-index over semantic-label following on NormBank in three models. In aggregate, MNLI favors extraction-index following, whereas Social Chemistry 101 (SC101) favors semantic-label following. Multiple-choice and open-ended evaluations can yield different behavioral conclusions. Thus, a steering gain under one answer encoding does not by itself identify what the intervention controls.

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Zhiwei Gao, Shaowen Peng, Shoko Wakamiya, Eiji Aramaki. 2026-08-24. What Does Activation Steering Control? Attribution Across Answer Encodings and Output-Sensitive Subspaces. https://arxiv.org/abs/2608.22985

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